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Re: [ksurf] more helium in sleds...

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  • Dave Culp
    ... Dave, this simply is not true. A cheapo aluminized mylar balloon holds helium at just over atmospheric for a week. There are *much* better films available,
    Message 1 of 8 , Jul 31, 2000
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      At 9:04 PM -0400 7/28/00, Dave Raue wrote:
      >But here are some facts: the atomic radius of He is about 1 angstom. Air
      >is mostly nitrogen, a nitrogen molecule is about 7 angstroms across. This
      >means that He is going to diffuse out of your bladder like mad. On an
      >atomic scale the baldder is quite porous, like microscopic chickenwire.
      >Chicken wire keeps the chickens in, but it doesn't do much to keep out the
      >mosquitos. Plasma metalization of the bladder perhaps? Otherwise, better
      >get the boys from duPont working on a new bladder material while you get
      >NASA or Hughes on the problems of valves that will work Even Robby and
      >Don, dieties though they may be, aren't likely to solve this one at a price
      >point that anyone who works for a living can afford.

      Dave, this simply is not true. A cheapo aluminized mylar balloon
      holds helium at just over atmospheric for a week. There are *much*
      better films available, even at very thin, thus light weights. Helium
      loss, at 5 lbs psig, of about 1% volume per day. At slightly higher
      weight, there are materials capable of containing helium for months.
      Believe it or not, there are others working on this engineering issue
      (other than wild and crazy kitesurfers!). Check out August's Wired
      magazine for an article on the rebirth of Zeppelin dirigibles. Or,
      check out any number of articles over the past few years, on long
      range, round-the-world balloons. All use helium, not hot air. They do
      not carry spare helium.

      Then, later:
      >I did more research on the subject I love to hate. Helium is
      >available from Fisher Scientific (among others). A 57 liter "lab
      >bottle" costs about $110. It's a small, portable, thermos-sized
      >pressure container. 57 liters means the volume at atmospheric
      >pressure is 57 l. Here's the arithmetic:
      >
      >1. Assume that an 11.5 m AR5 has a volume of 57 l (about 15 gallons,
      >doesn't seem so far off),
      >2. Assume that it needs to be inflated to 2 atmospheres (about 30 psi).
      >3. You need 2 bottles to do it, so this experiment will cost $220.

      Industrial helium (99.99% pure) costs about $55.00 US for 90 cu ft.,
      at one atmosphere. At this price, it comes in a 130 lb steel bottle.
      It is much cheaper in larger volumes. Nobody in their right mind
      would inflate a kite to 30 lbs pressure; try 1/2 to 3/4 lb, PSIG. For
      all intents and purposes, this is one atmosphere. It is only
      necessary to overcome the highest pressure the kite envelope will
      encounter due to aerodynamic forces, and that's what exists at the
      inflation window. For a really fast kite in big wind, this might be
      all of 1/4--1/2 lb, over atmospheric.

      (This is about the same you'd pressurize an air mattress to, by
      mouth, for example. I've yet to meet the man capable of 5lbs, PSIG,
      by mouth inflation. Doesn't mean there aren't several candidates
      here!)

      I think you dropped a decimal point, or maybe two, in your volume
      figures. If your kite is 11 sq meters, and is an average of 200 mm
      thick (about 8 inches), it's going to have 2.2 cubic meters of
      volume--that's 2200 liters (there are about 30 liters in a cubic
      foot...). Call it 73 cubic feet, or about 0.8 cylinders, at $55 a
      pop. Maybe $45-50 a fill-up. FWIW, 2.2 cubic meters of helium will
      float just under 5 lbs. Does your 11 meter kite, plus helium
      bladders, weigh less than that? If so it will fly in no wind. If not,
      it won't.

      >So the large economy size is far cheaper, but not very easy to bring
      >to the beach.

      This is correct. Life is not always "easy to bring to the beach."

      >My techno-weenie buds tell me a regular air compresser won't work
      >with Helium cause the atomic radius and density are too small. So
      >unless you want to carry around a lot of expensive, specialized gear
      >to capture the helium, each inflation is going to cost significant
      >bucks.

      This is also correct, but only partially. You *can* re-compress
      helium, with a positive displacement pump (ironically, this is the
      type of pump used by your diving buddies), but it'd be foolish to do
      so. It takes something like 8-10 hours to get 2200 lbs/sq in into a
      bottle with a diving compressor...

      You cannot pump helium with "squirrel cage" type compressors or fans.
      The molecule has too little mass; is too light weight (duh) for these
      to work effectively. Nothing to do with molecule size. Squirrel cage
      fans utilize centripedal force to move air. No mass, no centripedal
      force; no volume/pressure. (That's why a shop vacuum races when you
      block off its hose, rather than suck your hand inside out. You've
      deprived it of air to accelerate, so it becomes unloaded and just
      spins free. Don't try this with a positive displacement pump...)

      OK, OK. Physics in *small* bites. I get it... :-)

      Dave Culp
    • Dave Raue
      This is fun... ...More small bites... :-) ... angstom. Air ... across. This ... On an ... chickenwire. ... out the ... Otherwise, better ... you get ...
      Message 2 of 8 , Aug 1, 2000
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        This is fun... ...More small bites... :-)


        --- In kitesurf@egroups.com, Dave Culp <dave@d...> wrote:
        > At 9:04 PM -0400 7/28/00, Dave Raue wrote:
        > >But here are some facts: the atomic radius of He is about 1
        angstom. Air
        > >is mostly nitrogen, a nitrogen molecule is about 7 angstroms
        across. This
        > >means that He is going to diffuse out of your bladder like mad.
        On an
        > >atomic scale the baldder is quite porous, like microscopic
        chickenwire.
        > >Chicken wire keeps the chickens in, but it doesn't do much to keep
        out the
        > >mosquitos. Plasma metalization of the bladder perhaps?
        Otherwise, better
        > >get the boys from duPont working on a new bladder material while
        you get
        > >NASA or Hughes on the problems of valves that will work Even
        Robby and
        > >Don, dieties though they may be, aren't likely to solve this one
        at a price
        > >point that anyone who works for a living can afford.
        >
        > Dave, this simply is not true. A cheapo aluminized mylar balloon
        > holds helium at just over atmospheric for a week. There are *much*
        > better films available, even at very thin, thus light weights.
        Helium
        > loss, at 5 lbs psig, of about 1% volume per day. At slightly higher
        > weight, there are materials capable of containing helium for
        months.
        > Believe it or not, there are others working on this engineering
        issue
        > (other than wild and crazy kitesurfers!). Check out August's Wired
        > magazine for an article on the rebirth of Zeppelin dirigibles. Or,
        > check out any number of articles over the past few years, on long
        > range, round-the-world balloons. All use helium, not hot air. They
        do
        > not carry spare helium.

        I'm not sure which part isn't true. The point isn't that He can't be
        used, contained, compressed, etc. Obviously it can. It's that doing
        so in a practical, cost effective fashion isn't likely. Metalized
        mylar has pretty poor puncture resistance. And the context of the
        thread was as an inflation medium for Naish/Wipika designs. These
        have relatively small inflatable volumes that need to be at
        relatively high pressure since they provide structural support. It's
        pretty obvious that somebody could construct a sealed, inflatable
        foil. Making one that would survive sand fences, thorns, etc would
        be more challenging and expensive.

        > Then, later:
        > >I did more research on the subject I love to hate. Helium is
        > >available from Fisher Scientific (among others). A 57 liter "lab
        > >bottle" costs about $110. It's a small, portable, thermos-sized
        > >pressure container. 57 liters means the volume at atmospheric
        > >pressure is 57 l. Here's the arithmetic:
        > >
        > >1. Assume that an 11.5 m AR5 has a volume of 57 l (about 15
        gallons,
        > >doesn't seem so far off),
        > >2. Assume that it needs to be inflated to 2 atmospheres (about 30
        psi).
        > >3. You need 2 bottles to do it, so this experiment will cost $220.
        >
        > Industrial helium (99.99% pure) costs about $55.00 US for 90 cu
        ft.,
        > at one atmosphere. At this price, it comes in a 130 lb steel
        bottle.
        > It is much cheaper in larger volumes. Nobody in their right mind
        > would inflate a kite to 30 lbs pressure; try 1/2 to 3/4 lb, PSIG.
        For
        > all intents and purposes, this is one atmosphere. It is only
        > necessary to overcome the highest pressure the kite envelope will
        > encounter due to aerodynamic forces, and that's what exists at the
        > inflation window. For a really fast kite in big wind, this might be
        > all of 1/4--1/2 lb, over atmospheric.
        >
        > (This is about the same you'd pressurize an air mattress to, by
        > mouth, for example. I've yet to meet the man capable of 5lbs, PSIG,
        > by mouth inflation. Doesn't mean there aren't several candidates
        > here!)

        I hope I'm one of this rarefied group ;-)

        > I think you dropped a decimal point, or maybe two, in your volume
        > figures. If your kite is 11 sq meters, and is an average of 200 mm
        > thick (about 8 inches), it's going to have 2.2 cubic meters of
        > volume--that's 2200 liters (there are about 30 liters in a cubic
        > foot...). Call it 73 cubic feet, or about 0.8 cylinders, at $55 a
        > pop. Maybe $45-50 a fill-up. FWIW, 2.2 cubic meters of helium will
        > float just under 5 lbs. Does your 11 meter kite, plus helium
        > bladders, weigh less than that? If so it will fly in no wind. If
        not, it won't.

        I think not. The original thread was about inflatable sleds, not
        foils or flying mattresses. You're not suggesting that the volume of
        a 15m AR5 is 570 l or even 5700 l are you? Assume that a AR5
        bladders are about 20cm diam cylinder 5 meters long (for 15.5m??). I
        get a volume of about 37 l, even less than my estimate of 57 l. So,
        if 440 l he lifts a pound, then our 57 l will lift about 0.13 lbs. I
        guess the AR5 weighs more than that.
        As for pressure, I really don't know. What's the pressure in an
        AR5? Significantly more than an air mattress, that's for sure.

        > >So the large economy size is far cheaper, but not very easy to
        bring
        > >to the beach.
        >
        > This is correct. Life is not always "easy to bring to the beach."
        >
        > >My techno-weenie buds tell me a regular air compresser won't work
        > >with Helium cause the atomic radius and density are too small. So
        > >unless you want to carry around a lot of expensive, specialized
        gear
        > >to capture the helium, each inflation is going to cost significant
        > >bucks.
        >
        > This is also correct, but only partially.

        Not partially correct, completely correct (but only as far as it
        goes). But your explanation is more complete and the reason that
        helium recapture is impractical (unless you're in the blimp
        business)!!

        > You *can* re-compress
        > helium, with a positive displacement pump (ironically, this is the
        > type of pump used by your diving buddies), but it'd be foolish to
        do
        > so. It takes something like 8-10 hours to get 2200 lbs/sq in into a
        > bottle with a diving compressor...
        >
        > You cannot pump helium with "squirrel cage" type compressors or
        fans.
        > The molecule has too little mass; is too light weight (duh) for
        these
        > to work effectively. Nothing to do with molecule size. Squirrel cage

        Sorry, it has everything to do with molecule size. Size relates to
        electron configuration which relates to atomic number (as a glance at
        the periodic table will indicate) and both are lead to design
        considerations. A chemist will see the size and mass as interrelated
        functions of atomic weight and electron configuration. Tell him the
        size and he knows the mass. Perhaps an engineer can take the more
        simplified view of atoms/molecules as dimensionless point masses?
        Anyway, diffusion relates directly to size and influences valve,
        container, and material design (the chickenwire metaphor). In any
        case, taking a tire pump or sears air compressor to the beach ain't
        gonna work (which I guess you concur with?).

        > fans utilize centripedal force to move air. No mass, no centripedal
        > force; no volume/pressure. (That's why a shop vacuum races when you
        > block off its hose, rather than suck your hand inside out. You've
        > deprived it of air to accelerate, so it becomes unloaded and just
        > spins free. Don't try this with a positive displacement pump...)
        >
        > OK, OK. Physics in *small* bites. I get it... :-)

        Bring it on dude, bring it on!! :-)) (I admit, my arithmetic sucks!)
        >
        > Dave Culp
      • Dave Culp
        ... Guess I m going to have to ask you for some definitions, Dave. Yes, the thread is more helium in sleds. OK, I guess I ll grant you that Naish s are
        Message 3 of 8 , Aug 1, 2000
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          Dave Raue:
          >I'm not sure which part isn't true. The point isn't that He can't be
          >used, contained, compressed, etc. Obviously it can. It's that doing
          >so in a practical, cost effective fashion isn't likely. Metalized
          >mylar has pretty poor puncture resistance. And the context of the
          >thread was as an inflation medium for Naish/Wipika designs. These
          >have relatively small inflatable volumes that need to be at
          >relatively high pressure since they provide structural support. It's
          >pretty obvious that somebody could construct a sealed, inflatable
          >foil. Making one that would survive sand fences, thorns, etc would
          >be more challenging and expensive.

          Guess I'm going to have to ask you for some definitions, Dave. Yes,
          the thread is "more helium in sleds." OK, I guess I'll grant you that
          Naish's are "sleds," though I can find no reference work that so
          defines them (including both Wipika's and Naish's web sites) And yes,
          we established, long ago, that trying to get any value from putting
          helium into the tubes of a Naish or Wipika was a *total* waste of
          time. You're better off putting helium in your bike's tires, then
          trying to fly the bike. We've *covered* all this, in this
          interminable thread. Forgive me, I was under the impression we'd
          moved on, and were discussing putting helium into any *other* types
          of kites, where it might be actually, physically possible for it to
          have some effect.

          Having said that, we (you!) were discussing 1) permeability of
          fabric, and the general expense/impossibility of same, and 2)
          re-compressing helium via mechanical pumps. (Is anyone else on the
          same page? Is anyone else even listening??)

          If I were asked to build a helium-filled kite, I wouldn't use a
          single bit of either fabric or film, but a combination, just as
          inflatable boats use (plastic bladder, inside fabric cells). In fact,
          I *have* done this, with good results. No, I'm not going to teach you
          how to do it, nor reveal my suppliers to you. Sorry.

          Now, you said:
          >... He is going to diffuse out of your bladder like mad. On an
          >atomic scale the baldder is quite porous, like microscopic
          >chickenwire. Chicken wire keeps the chickens in, but it doesn't do
          >much to keep out the mosquitos. Plasma metalization of the bladder
          >perhaps? Otherwise, better get the boys from duPont working on a new
          >bladder material...

          From this, I presume you are talking about bladder material, and
          about helium permeability, of bladder material. Sorry to be pedantic,
          but you keep changing the subject. Real, cheap films already exist,
          they do not need to be developed (I expect DuPont makes some, but I
          haven't checked; I use another manufacturer). They are relatively
          *very* impervious to small molecules, such as helium; much better
          than aluminized mylar, for instance. Weights on the order of half an
          oz/yard can be had. Unsuitable for kitemaking; we're talking about
          *bladder* material (see above; your words, Dave).

          To inflation pressures. I hope we've already determined the issue of
          Naish/Wipika inflation pressures to be moot, with any relation to
          helium, but for what it's worth, I think I answered that one, too. By
          mouth, you are physically unable to exceed about 5 lbs. Certainly 30
          lbs is silly--you put that much in your automobile, then carry 4-5000
          pounds of car around, on 4 little half sq ft patches. It's not
          necessary to argue the point, though. You've got the kite? A pressure
          guage's less than $20 at any hardware store. If you unwrap it
          carefully, you could likely return it for a refund after you measure
          the pressure in your Naish.

          > > I've yet to meet the man capable of 5lbs, PSIG,
          > > by mouth inflation. Doesn't mean there aren't several candidates
          > > here!)
          >
          >I hope I'm one of this rarefied group ;-)

          Well, yes, now you mention it... :-)

          >I think not. The original thread was about inflatable sleds, not
          >foils or flying mattresses. You're not suggesting that the volume of
          >a 15m AR5 is 570 l or even 5700 l are you?

          Well, yes, I am going to suggest you've made yet another arithmetic
          error. Sorry. ;-)

          >Assume that a AR5
          >bladders are about 20cm diam cylinder 5 meters long (for 15.5m??). I
          >get a volume of about 37 l, even less than my estimate of 57 l.

          A "square" tube (no taper) 20 cm by 5 meters will contain about 0.157
          cubic meters, or 157 liters. I've never measured an AR5, but suspect
          the average tube diameter is a good bit more than 8" (20cm). Perhaps
          you took the number from me? I was referring to an average thickness,
          for a foil.

          >>You cannot pump helium with "squirrel cage" type compressors or
          >>fans. The molecule has too little mass; is too light weight (duh)
          >>for these to work effectively. Nothing to do with molecule size.
          >>Squirrel cage

          >Sorry, it has everything to do with molecule size. Size relates to
          >electron configuration which relates to atomic number (as a glance at
          >the periodic table will indicate) and both are lead to design
          >considerations. A chemist will see the size and mass as interrelated
          >functions of atomic weight and electron configuration. Tell him the
          >size and he knows the mass. Perhaps an engineer can take the more
          >simplified view of atoms/molecules as dimensionless point masses?
          >Anyway, diffusion relates directly to size and influences valve,
          >container, and material design (the chickenwire metaphor). In any
          >case, taking a tire pump or sears air compressor to the beach ain't
          >gonna work (which I guess you concur with?).

          Back to semantics again. We seemed changed the subject (*you* changed
          the subject), away from fabric permeability, to compressibility and
          handling of gasses inside metal devices (pumps). I thought I was
          being pedantic again, but if you'll read your own post, Dave, you
          stopped talking about permeability, and switched to gas compression.
          My comments relate to gas handling, not fabric, which I covered
          earlier.

          Let's not split hairs, though: Sure, you're right, molecule size is
          all important, with regards to fabric permeability. OTOH, your
          chemistry lesson holds little water, and demonstrates why chemists
          don't build kites. Which is smaller, Dave, a molecule of helium or a
          molecule of hydrogen? A molecule of ordinary air, or of water?
          (*answers at the end of the post. Don't cheat--give it a guess before
          you look!)

          Last, FWIW, I *do* take an oversized tire pump to the beach. I use it
          for sucking gas *out* of the kite, and exhausting it onto the
          atmosphere.

          > > OK, OK. Physics in *small* bites. I get it... :-)
          >
          >Bring it on dude, bring it on!! :-))

          OK. Hydrogen, when it exists as a pure gas, is a diatomic molecule.
          That is, it's two atoms, connected together. Helium, which is inert,
          is a monatomic molecule--a single atom, floating free. Though
          physically, a hydrogen atom is of smaller diameter than a helium atom
          (though nowhere near 1/2 the size, as its atomic weight might suggest
          to Dave's chemist), two hydrogen molecules connected together are
          quite a bit larger than a single helium atom, so the first answer is
          "helium."

          Similarly, both oxygen and nitrogen, which together make up about
          98-99% of air, are diatomic molecules. Two atoms of oxy or two atoms
          of nitrogen, always connected together. Water, H2O, has three atoms,
          but it's a biggish oxygen atom, connected to two tiny hydrogen atoms.
          Overall, the water molecule is smaller than either oxygen or nitrogen
          molecules. Yes, there are devices which are demonstrably "air-tight"
          and yet will leak water. Usually water vapor, but the stuff gets in
          and wreaks havoc with fine instruments and connections, even so.

          You don't need to take my word on either of these; ask any
          high-school or college chemistry teacher.

          Dave Culp
        • Dave Raue
          Great Ceaser s ghost! Somebody even more pedantic than I am!! I wonder how long it will be before the flames start for us to take this nitpicking private.
          Message 4 of 8 , Aug 1, 2000
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            Great Ceaser's ghost! Somebody even more pedantic than I am!! I wonder how
            long it will be before the flames start for us to take this nitpicking
            private. Well, not a peep so far, so I guess I'll have at it some more....

            ----- Original Message -----
            From: "Dave Culp" <dave@...>
            To: <kitesurf@egroups.com>
            Sent: Tuesday, August 01, 2000 6:34 PM
            Subject: [ksurf] Re: more helium in sleds...


            > Dave Raue:
            > >I'm not sure which part isn't true. The point isn't that He can't be
            > >used, contained, compressed, etc. Obviously it can. It's that doing
            > >so in a practical, cost effective fashion isn't likely. Metalized
            > >mylar has pretty poor puncture resistance. And the context of the
            > >thread was as an inflation medium for Naish/Wipika designs. These
            > >have relatively small inflatable volumes that need to be at
            > >relatively high pressure since they provide structural support. It's
            > >pretty obvious that somebody could construct a sealed, inflatable
            > >foil. Making one that would survive sand fences, thorns, etc would
            > >be more challenging and expensive.
            >
            > Guess I'm going to have to ask you for some definitions, Dave. Yes,
            > the thread is "more helium in sleds." OK, I guess I'll grant you that
            > Naish's are "sleds," though I can find no reference work that so
            > defines them (including both Wipika's and Naish's web sites) And yes,
            > we established, long ago, that trying to get any value from putting
            > helium into the tubes of a Naish or Wipika was a *total* waste of
            > time. You're better off putting helium in your bike's tires, then
            > trying to fly the bike. We've *covered* all this, in this
            > interminable thread. Forgive me, I was under the impression we'd
            > moved on, and were discussing putting helium into any *other* types
            > of kites, where it might be actually, physically possible for it to
            > have some effect.

            Well, we had, but I got on a tear and resurrected it. Nice analogy with the
            bike tire, though. Whoever raised it most recently didn't seem to have read
            the archives. In fact this has been covered several years ago in rec.kites
            if I remember right.

            > Having said that, we (you!) were discussing 1) permeability of
            > fabric, and the general expense/impossibility of same, and 2)
            > re-compressing helium via mechanical pumps. (Is anyone else on the
            > same page? Is anyone else even listening??)

            It doesn't matter if WE'RE having fun with this....

            > If I were asked to build a helium-filled kite, I wouldn't use a
            > single bit of either fabric or film, but a combination, just as
            > inflatable boats use (plastic bladder, inside fabric cells). In fact,
            > I *have* done this, with good results. No, I'm not going to teach you
            > how to do it, nor reveal my suppliers to you. Sorry.

            Going the composite route seems like a pretty obvious step for an engineer.
            Don't worry, I'm not going to try it.

            > Now, you said:
            > >... He is going to diffuse out of your bladder like mad. On an
            > >atomic scale the baldder is quite porous, like microscopic
            > >chickenwire. Chicken wire keeps the chickens in, but it doesn't do
            > >much to keep out the mosquitos. Plasma metalization of the bladder
            > >perhaps? Otherwise, better get the boys from duPont working on a new
            > >bladder material...
            >
            > From this, I presume you are talking about bladder material, and
            > about helium permeability, of bladder material. Sorry to be pedantic,
            > but you keep changing the subject.

            YES! The world presents so many interesting challenges! This is what makes
            me such a fascinating fellow.

            > Real, cheap films already exist,
            > they do not need to be developed (I expect DuPont makes some, but I
            > haven't checked; I use another manufacturer). They are relatively
            > *very* impervious to small molecules, such as helium; much better
            > than aluminized mylar, for instance. Weights on the order of half an
            > oz/yard can be had. Unsuitable for kitemaking; we're talking about
            > *bladder* material (see above; your words, Dave)

            Well, in principle we seem to be on the same wavelength. So I now fall back
            to the context, not a dissertation on what is possible. The context is sled
            kites. Would any of the appropriately impermeable films have the palette of
            physical properties needed to serve as a drop-in replacement for the Naish
            bladder? I don't know, but I'd be surprised if they could endure the
            mechanical abuses as well as HDPE or PVC or whatever they use. But I
            haven't given the matter serious study.

            > To inflation pressures. I hope we've already determined the issue of
            > Naish/Wipika inflation pressures to be moot, with any relation to
            > helium, but for what it's worth, I think I answered that one, too. By
            > mouth, you are physically unable to exceed about 5 lbs. Certainly 30
            > lbs is silly--you put that much in your automobile, then carry 4-5000
            > pounds of car around, on 4 little half sq ft patches. It's not
            > necessary to argue the point, though.

            But I'll argue it anyway since I don't like your analogy :-) I put 120 psi
            into my bike tire and load it with 200 lbs. That's 4x the pressure for 1/8
            the load. And I'll bet I could do it by mouth if Todd were egging me on.

            > You've got the kite? A pressure
            > guage's less than $20 at any hardware store. If you unwrap it
            > carefully, you could likely return it for a refund after you measure
            > the pressure in your Naish.
            >
            > > > I've yet to meet the man capable of 5lbs, PSIG,
            > > > by mouth inflation. Doesn't mean there aren't several candidates
            > > > here!)
            > >
            > >I hope I'm one of this rarefied group ;-)
            >
            > Well, yes, now you mention it... :-)

            See above.... fortunately I've got plenty of company.. :-)

            > >I think not. The original thread was about inflatable sleds, not
            > >foils or flying mattresses. You're not suggesting that the volume of
            > >a 15m AR5 is 570 l or even 5700 l are you?
            >
            > Well, yes, I am going to suggest you've made yet another arithmetic
            > error. Sorry. ;-)

            Quite possible, thank god I'm not designing bridges!

            > >Assume that a AR5
            > >bladders are about 20cm diam cylinder 5 meters long (for 15.5m??). I
            > >get a volume of about 37 l, even less than my estimate of 57 l.
            >
            > A "square" tube (no taper) 20 cm by 5 meters will contain about 0.157
            > cubic meters, or 157 liters. I've never measured an AR5, but suspect
            > the average tube diameter is a good bit more than 8" (20cm). Perhaps
            > you took the number from me? I was referring to an average thickness,
            > for a foil.

            Yeah, whatever, we can move the decimal around a lot and the AR5 still won't
            float. I guess we agree on that.

            > >>You cannot pump helium with "squirrel cage" type compressors or
            > >>fans. The molecule has too little mass; is too light weight (duh)
            > >>for these to work effectively. Nothing to do with molecule size.
            > >>Squirrel cage
            >
            > >Sorry, it has everything to do with molecule size. Size relates to
            > >electron configuration which relates to atomic number (as a glance at
            > >the periodic table will indicate) and both are lead to design
            > >considerations. A chemist will see the size and mass as interrelated
            > >functions of atomic weight and electron configuration. Tell him the
            > >size and he knows the mass. Perhaps an engineer can take the more
            > >simplified view of atoms/molecules as dimensionless point masses?
            > >Anyway, diffusion relates directly to size and influences valve,
            > >container, and material design (the chickenwire metaphor). In any
            > >case, taking a tire pump or sears air compressor to the beach ain't
            > >gonna work (which I guess you concur with?).
            >
            > Back to semantics again. We seemed changed the subject (*you* changed
            > the subject), away from fabric permeability, to compressibility and
            > handling of gasses inside metal devices (pumps). I thought I was
            > being pedantic again, but if you'll read your own post, Dave, you
            > stopped talking about permeability, and switched to gas compression.
            > My comments relate to gas handling, not fabric, which I covered
            > earlier.

            Obviously you thought you had pedantry all locked up. Sorry, you lose. And
            I'm undisiplined too! ;-) Anyway, my object wasn't a technical symposium
            on the design challenges of lighter-than-air kites. Seriously though, your
            cogent contributions to the group have been authoritative and informative.
            But it's a mistake to take my rants too seriously (unless it's about
            patents).

            > Let's not split hairs, though: Sure, you're right, molecule size is
            > all important, with regards to fabric permeability. OTOH, your
            > chemistry lesson holds little water, and demonstrates why chemists
            > don't build kites. Which is smaller, Dave, a molecule of helium or a
            > molecule of hydrogen? A molecule of ordinary air, or of water?
            > (*answers at the end of the post. Don't cheat--give it a guess before
            > you look!)
            >
            > Last, FWIW, I *do* take an oversized tire pump to the beach. I use it
            > for sucking gas *out* of the kite, and exhausting it onto the
            > atmosphere.
            >
            > > > OK, OK. Physics in *small* bites. I get it... :-)
            > >
            > >Bring it on dude, bring it on!! :-))
            >
            > OK. Hydrogen, when it exists as a pure gas, is a diatomic molecule.
            > That is, it's two atoms, connected together. Helium, which is inert,
            > is a monatomic molecule--a single atom, floating free. Though
            > physically, a hydrogen atom is of smaller diameter than a helium atom
            > (though nowhere near 1/2 the size, as its atomic weight might suggest
            > to Dave's chemist), two hydrogen molecules connected together are
            > quite a bit larger than a single helium atom, so the first answer is
            > "helium."
            >
            > Similarly, both oxygen and nitrogen, which together make up about
            > 98-99% of air, are diatomic molecules. Two atoms of oxy or two atoms
            > of nitrogen, always connected together. Water, H2O, has three atoms,
            > but it's a biggish oxygen atom, connected to two tiny hydrogen atoms.
            > Overall, the water molecule is smaller than either oxygen or nitrogen
            > molecules. Yes, there are devices which are demonstrably "air-tight"
            > and yet will leak water. Usually water vapor, but the stuff gets in
            > and wreaks havoc with fine instruments and connections, even so.
            >
            > You don't need to take my word on either of these; ask any
            > high-school or college chemistry teacher.

            You know not with whom you are dealing, Dr Culp. The chemist would never be
            taken in by this sophistry. Now it is you who must define your terms. As
            you're doubtless aware, atomic radii can only be interpreted in the context
            of electron configuration and chemical bonding (if any, none for helium).
            The crystal radii of hydrogen and helium are, respectively, 0.25 and 1.53
            angstroms. Yet the orbital radii are 0.53 and 0.29 angstroms. So,
            presumably you refer to crystal radii. Yet, for diatomic hydrogen, the
            Heitler-London treatment gives an internuclear distance of 0.742 angstroms,
            smaller than crystal radius of helium. As you correctly point out, atomic
            hydrogen doesn't really exist in nature since its electronic configuration
            isn't stable. Since the chemist knows all this, and is versed in molecular
            orbital theory, only the high school teacher (or professor, depending on
            where...) would infer that hydrogen is half the size of helium based on
            atomic weight. As for diffusion, molecular size is only one factor (which I
            guess you know full well). Polarity, electron configuration, partial
            pressures, etc all play a role too, sometimes an even greater one. But all
            other things equal, size matters (which I also guess you know full well).

            This has been fun, and a nice diversion while on tedious phone calls. But
            soon I'll have to start doing real research to carry on. I therefore resign
            from this thread and hope it has entertained you as well. (But don't
            provoke me further or I'll be forced to invoke my buddies who are REAL
            scientists, not posers like me :-))

            -Dave Raue
          • Dave Culp
            ... Yes. ... Apparently. Dave Culp
            Message 5 of 8 , Aug 2, 2000
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              > > Real, cheap films already exist,
              > > they do not need to be developed (I expect DuPont makes some, but I
              > > haven't checked; I use another manufacturer). They are relatively
              > > *very* impervious to small molecules, such as helium; much better
              > > than aluminized mylar, for instance. Weights on the order of half an
              > > oz/yard can be had. Unsuitable for kitemaking; we're talking about
              > > *bladder* material (see above; your words, Dave)
              >
              >Well, in principle we seem to be on the same wavelength. So I now fall back
              >to the context, not a dissertation on what is possible. The context is sled
              >kites. Would any of the appropriately impermeable films have the palette of
              >physical properties needed to serve as a drop-in replacement for the Naish
              >bladder?

              Yes.

              >I don't know... snip... I
              >haven't given the matter serious study.

              Apparently.

              Dave Culp
            • Dave Raue
              A fitting end to this increasingly preposterous exchange. Very clever, Dr Culp. But I will be watching... :-) -Dave ... From: Dave Culp
              Message 6 of 8 , Aug 2, 2000
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                A fitting end to this increasingly preposterous exchange. Very clever, Dr
                Culp. But I will be watching... :-)

                -Dave
                ----- Original Message -----
                From: "Dave Culp" <dave@...>
                To: <kitesurf@egroups.com>
                Sent: Wednesday, August 02, 2000 12:40 PM
                Subject: Re: [ksurf] Re: more helium in sleds...


                > > > Real, cheap films already exist,
                > > > they do not need to be developed (I expect DuPont makes some, but I
                > > > haven't checked; I use another manufacturer). They are relatively
                > > > *very* impervious to small molecules, such as helium; much better
                > > > than aluminized mylar, for instance. Weights on the order of half an
                > > > oz/yard can be had. Unsuitable for kitemaking; we're talking about
                > > > *bladder* material (see above; your words, Dave)
                > >
                > >Well, in principle we seem to be on the same wavelength. So I now fall
                back
                > >to the context, not a dissertation on what is possible. The context is
                sled
                > >kites. Would any of the appropriately impermeable films have the palette
                of
                > >physical properties needed to serve as a drop-in replacement for the
                Naish
                > >bladder?
                >
                > Yes.
                >
                > >I don't know... snip... I
                > >haven't given the matter serious study.
                >
                > Apparently.
                >
                > Dave Culp
                >
                >
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              • tim clark
                Just saw a 3 minute piece on Manu Bertin flying a sled around the cold waters of Greenland inlated by helium. Seemed to work for those light wind days. The
                Message 7 of 8 , Aug 14, 2000
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                  Just saw a 3 minute piece on Manu Bertin flying a sled around
                  the cold waters of Greenland inlated by helium. Seemed to work
                  for those light wind days. The down side of this was the cold
                  could make him lose his senses quicker resulting in fallin in. No
                  shots of water relaunching though. The icebergs looked great!!!
                  Tim
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